57 research outputs found
Kohn Anomalies in Superconductors
I present the detailed behavior of phonon dispersion curves near momenta
which span the electronic Fermi sea in a superconductor. I demonstrate that an
anomaly, similar to the metallic Kohn anomaly, exists in a superconductor's
dispersion curves when the frequency of the phonon spanning the Fermi sea
exceeds twice the superconducting energy gap. This anomaly occurs at
approximately the same momentum but is {\it stronger} than the normal-state
Kohn anomaly. It also survives at finite temperature, unlike the metallic
anomaly. Determination of Fermi surface diameters from the location of these
anomalies, therefore, may be more successful in the superconducting phase than
in the normal state. However, the superconductor's anomaly fades rapidly with
increased phonon frequency and becomes unobservable when the phonon frequency
greatly exceeds the gap. This constraint makes these anomalies useful only in
high-temperature superconductors such as .Comment: 18 pages (revtex) + 11 figures (upon request), NSF-ITP-93-7
The formation, properties and impact of secondary organic aerosol: current and emerging issues
Secondary organic aerosol (SOA) accounts for
a significant fraction of ambient tropospheric aerosol and a
detailed knowledge of the formation, properties and transformation
of SOA is therefore required to evaluate its impact
on atmospheric processes, climate and human health.
The chemical and physical processes associated with SOA
formation are complex and varied, and, despite considerable
progress in recent years, a quantitative and predictive
understanding of SOA formation does not exist and therefore
represents a major research challenge in atmospheric
science. This review begins with an update on the current
state of knowledge on the global SOA budget and is followed
by an overview of the atmospheric degradation mechanisms
for SOA precursors, gas-particle partitioning theory
and the analytical techniques used to determine the chemical
composition of SOA. A survey of recent laboratory,
field and modeling studies is also presented. The following
topical and emerging issues are highlighted and discussed
in detail: molecular characterization of biogenic SOA constituents,
condensed phase reactions and oligomerization, the
interaction of atmospheric organic components with sulfuric
acid, the chemical and photochemical processing of organics
in the atmospheric aqueous phase, aerosol formation
from real plant emissions, interaction of atmospheric organic
components with water, thermodynamics and mixtures in atmospheric
models. Finally, the major challenges ahead in
laboratory, field and modeling studies of SOA are discussed
and recommendations for future research directions are proposed
Phylogenomic analysis of a 55.1 kb 19-gene dataset resolves a monophyletic Fusarium that includes the Fusarium solani Species Complex
Scientific communication is facilitated by a data-driven, scientifically sound taxonomy that considers the end-user¿s needs and established successful practice. In 2013, the Fusarium community voiced near unanimous support for a concept of Fusarium that represented a clade comprising all agriculturally and clinically important Fusarium species, including the F. solani species complex (FSSC). Subsequently, this concept was challenged in 2015 by one research group who proposed dividing the genus Fusarium into seven genera, including the FSSC described as members of the genus Neocosmospora, with subsequent justification in 2018 based on claims that the 2013 concept of Fusarium is polyphyletic. Here, we test this claim and provide a phylogeny based on exonic nucleotide sequences of 19 orthologous protein-coding genes that strongly support the monophyly of Fusarium including the FSSC. We reassert the practical and scientific argument in support of a genus Fusarium that includes the FSSC and several other basal lineages, consistent with the longstanding use of this name among plant pathologists, medical mycologists, quarantine officials, regulatory agencies, students, and researchers with a stake in its taxonomy. In recognition of this monophyly, 40 species described as genus Neocosmospora were recombined in genus Fusarium, and nine others were renamed Fusarium. Here the global Fusarium community voices strong support for the inclusion of the FSSC in Fusarium, as it remains the best scientific, nomenclatural, and practical taxonomic option availabl
Aspergillus species recombinant antigens for serodiagnosis of farmer's lung disease.
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